The simplest most common interface between a client and server occurs when the client and server are linked into the same process. In this case, the client can invoke a subroutine call to access the server. Calling Input Parameters can be passed from the client to the server in common memory and Returned Output Parameters can be passed back from the server to the client through common memory to complete the call.
To utilize the power of distributed computing architecture, it is necessary that the server frequently reside in a network node which is remote from the client node. Multiple clients may be requesting the same service from multiple servers at the same time. In additiona, there is a requirement in telephony applications for both hardware and software redundancy to provide a hardware/software fault tolerant service environment. This environment consists of nodes in geographically remote locations in the global telecommunications network. The system must be able to quickly adjust to server outages at any point in the network.